Protein Flocculation Induced by Sodium Polyacrylate

In the processing of frozen minced fish meat represented by haddock, the processing wastewater contains water-soluble proteins. These water-soluble proteins can be quickly coagulated by adding sodium polyacrylate aqueous solution to recover edible proteins.

Application Principle

After removing the floating fat in the fish washing water, hydrochloric acid is added to the remaining wastewater until the isoelectric point of the fish protein is reached, so that the pH value of the wastewater is lowered. Then, the protein dissolved in the water in a colloid state is made into an unstable colloid. If a 0.1% sodium polyacrylate aqueous solution is added to it, the fish protein will immediately condense and form a whole block. In the condensed block, pressurized water that has been blown into air to a point close to the saturation point is injected. Then, the condensate floats up and forms a scum called "bubble", which is scooped up with a scraper. After the "bubble" is concentrated and dehydrated, the recovered protein is used as feed, and the waste liquid becomes a clear liquid. In Figure 1, the optimal addition amount of sodium polyacrylate is 30ppm. If this amount is exceeded, dispersion will occur and the volume of the sediment will increase.

0.1% sodium polyacrylate aqueous solution addition amount

Fig.1 Precipitation efficiency of free protein in the supernatant of horse mackerel processing water

Mechanism of the coalescence reaction between proteins and sodium polyacrylate

In alkaline conditions, the amino group dissociation is inhibited, and the amino acids in the protein components show anionic properties. However, when the isoelectric point is acidic, it becomes a cation ( ). Therefore, sodium polyacrylate can easily form ionic bonds with protein molecules at the isoelectric point, as shown in Figure 2.

Figure 2 Protein flocculation mechanism

Note: All food protein flocculation and recovery requirements are the same